1. Field of the Invention
The present invention relates to a plasma display panel. More particularly, the present invention relates to a plasma display panel with an improved structure that can enhance brightness and bright room contrast.
2. Description of the Related Art
A plasma display panel (PDP) is an apparatus that forms an image using an electrical discharge, and has superior display performances in brightness and viewing angle. In such a PDP, a DC or AC voltage applied to electrodes causes a gas discharge between the electrodes, and ultraviolet rays generated during the gas discharge excites phosphors, so that visible light is emitted from the excited fluorescent material.
The PDP can be classified into either a DC type PDP or an AC type PDP according to the type of gas discharge. The DC type PDP has a structure in which all electrodes are exposed to a discharge space and charges move directly between the electrodes. The AC type PDP has a structure in which at least one electrode is covered with a dielectric layer, and charges do not move directly between the corresponding electrodes but discharge is performed by wall charges.
Alternatively, the PDP may be classified into either a facing discharge type PDP or a surface discharge type PDP according to the arrangement structure of the electrodes. The facing discharge type PDP has a structure in which two sustaining electrodes forming a pair are formed respectively on a lower substrate and an upper substrate, and a discharge occurs in a direction perpendicular to the substrate. The surface discharge type PDP has a structure in which two sustaining electrodes forming a pair are respectively formed on the same substrate, and a discharge occurs in a direction parallel to the substrate.
The facing discharge type PDP has a high luminous efficiency, but it has also a disadvantage in that the fluorescent phosphor layer is easily degenerated. To this end, at present, the surface discharge type PDP is mainly used.
FIGS. 1 and 2 show a construction of a general surface discharge type PDP. Particularly, FIG. 2 shows that only an upper substrate of the surface discharge type PDP is rotated by 90 degrees for easier understanding of an inner structure of the PDP.
Referring to FIGS. 1 and 2, the conventional PDP includes a lower substrate 10 and an upper substrate 20 facing each other.
On an upper surface of the lower substrate 10, a plurality of address electrodes 11 are arranged in a stripe configuration. The address electrodes 11 are buried by a first dielectric layer 12. On the first dielectric layer 12, a plurality of barrier ribs 13 are formed spaced away by a predetermined distance from one another so as to prevent electrical and optical cross-talk between discharge cells 14. The inner surfaces of discharge cells 14 are partitioned by the barrier ribs 13 and are coated with a predetermined thickness of a red (R), green (G) and blue (B) fluorescent layer 15. Inside the discharge cells 14, a discharge gas is filled. The discharge gas is a mixture gas of neon (Ne) gas and a small amount of xenon (Xe) gas, which is generally used for a plasma discharge.
The upper substrate 20 is a transparent substrate through which visible light passes, and is formed mainly of glass. The upper substrate 20 is coupled with the lower substrate 10 having the barrier ribs 13. On a lower surface of the upper substrate 20, sustaining electrodes 21a and 21b forming pairs and perpendicularly crossing the address electrodes 11 are arranged in a stripe configuration. The sustaining electrodes 21a and 21b are formed of a transparent conductive material such as indium tin oxide (ITO) such that the visible light can pass through the sustaining electrodes 21a and 21b. In order to reduce a line resistance of the sustaining electrodes 21a and 21b, bus electrodes 22a and 22b formed of a metal are formed beneath the respective sustaining electrodes 21a and 21b at a width less than that of the sustaining electrodes 21a and 21b. These sustaining electrodes 21a and 21b and the bus electrodes 22a and 22b are covered with a second dielectric layer 23. Beneath the second dielectric layer 23, a protective layer 24 is formed. The protective layer 24 prevents the second dielectric layer 23 from being damaged due to a sputtering of plasma particles and emits secondary electrons, thereby lowering the discharge voltage. The protective layer 24 is generally formed of magnesium oxide (MgO). Meanwhile, a plurality of black stripes 30 are formed spaced away by a predetermined distance from one another in parallel with the sustaining electrodes 21a and 21b on an upper surface of the upper substrate 20 so as to prevent light from being introduced into the panel from the exterior.
The operation of the conventional PDP constructed as above is generally classified into an operation for an address discharge and an operation for the sustaining discharge. The address discharge occurs between the address electrodes 11 and any one of the sustaining electrodes 21a and 21b, and during the address discharge, wall charges are formed. The sustaining discharge occurs due to a potential difference between the sustaining electrodes 21a and 21b positioned at the discharge cells 14 in which the wall charges are formed. During the sustaining discharge, the fluorescent layer 15 of the corresponding discharge cell is excited by ultraviolet rays generated from the discharge gas, so that visible light is emitted. When this visible light passes through the upper substrate 20, an image that is conceivable by a user is formed.
However, in the conventional PDP constructed as above, when the exterior is in a bright condition, namely, in a bright room condition, exterior light is introduced into the discharge cells 14, so that the introduced light overlaps the light generated from the discharge cells 14. As a result, the bright room contrast is lowered and thus the image display performance of the PDP is deteriorated.